I think one of the main issues is that Vulkan is really bad from a usability perspective. OpenGL is too, but there is little incentive to switch from one bad API that you know how to use, to another bad API that you don't know how to use. On the other hand, I've spent time learning WebGPU in the past year and found that it was an excellent API that is an enormous quality of live improvement over OpenGL, so even if it has fewer features (due to Web, not API design), it's still something that I really want to switch to, unlike Vulkan.